It’s well known that norovirus is highly contagious, especially in long-term care facilities. But new research shows that it may be even more transmissible than previously thought.

A study published this month in Clinical Infectious Diseases showed that norovirus GII1  – the most common norovirus genogroup2  – is often present in the air at health care facilities during outbreaks of the virus. In vitro studies also suggest that the virus may be able to withstand aerosolization.3

The researchers took air samples from eight health care facilities around Quebec City, Canada, during active outbreaks of norovirus GII. Norovirus GII genomes were detected in six of those facilities. In patients showing symptoms, norovirus RNA was found in more than half of those patients’ rooms. It was also found in six of 16 hallways and in three of six nurses’ stations. 4

The results demonstrate how easily norovirus can be contracted, said Caroline Duchaine, PhD, a professor at Laval University and an author of the study. “It suggests that exposure may occur even when [health care] workers are not in the presence of virus-shedding patients,” said Duchaine.

Norovirus Seems to Survive Aerolization

The study also evaluated whether norovirus can stay intact when subjected to the stresses of aerosolization, as happens when patients vomit or cough, or when a toilet is flushed. Because norovirus GII is difficult to culture, a similar virus (the murine norovirus MNV-1) was used instead. 

After aerosolizing the virus in an aerosol chamber, researchers found that the concentration of the virus was not altered significantly. 

“This model suggests that norovirus remains infectious during its journey in the aerosol state,” said Duchaine.

The results of the study may be especially important for physicians who work in long-term care facilities like nursing homes, which have unique characteristics that make norovirus transmission more likely. 

“There’s a high level of contact between residents and professionals who are providing care for them,” said Benjamin Lopman, PhD, an epidemiologist with the Centers for Disease Control and Prevention (CDC) in Atlanta. “Also, because many people in nursing homes may have mental disabilities, they may also have compromised hygiene. Norovirus can be very difficult to control with those kinds of populations.”

Figures from the CDC show that 80% of all nonfoodborne norovirus outbreaks in the United States from 2009 to 2012 occurred in long-term care facilities. 

Are Existing Precautions Enough?

To control and prevent norovirus outbreaks, Lopman said, physicians who work in nursing home settings should implement the CDC’s current recommendations, which include thorough hand washing with soap and water (for at least 20 seconds) and limiting bare-hand contact with foods that are ready to eat. Patients infected with norovirus should also be isolated during the acute phase of their illness and for up to 72 hours afterward.

It may also be advisable to implement so-called “barrier nursing” techniques, which would require staff members to wear protective gowns and gloves when in contact with an infected patient, Lopman said. To remove the virus from the environment, disinfecting commonly touched surfaces with a chlorine bleach solution is recommended.

However, according to Duchaine, in light of the new study’s findings, it may be necessary to implement additional precautions to limit airborne spread of norovirus. This might include having staff members use respirators, closing infected patients’ doors, and even using negative-pressure rooms.

But Lopman says more evidence is needed before those protocols become standard. “The precautions we have are generally effective at containing outbreaks,” Lopman says. “We’re always monitoring things and updating our recommendations once new evidence becomes available.”

Medically reviewed by Pat F. Bass III, MD, MS, MPH      

References

1.  Detection and Quantification of Airborne Norovirus During Outbreaks in Healthcare Facilities. Clin Infect Dis. 2015 Aug 1;61(3):299-304..

2.  Norovirus, Clinical Overview.

3.  Vital Signs: Foodborne Norovirus Outbreaks — United States, 2009–2012.

4.  Updated Norovirus Outbreak Management and Disease Prevention Guidelines.